The present invention relates generally to the field of golf clubs and more particularly to the manufacture of metal "wood" club heads.
It is well known that accuracy and distance are the two primary concerns when making golf shots with a "wood" type club (hereinafter referred to as "wood" or "woods"), such as a driver or a fairway wood. Accuracy and distance are inter-related in the sense that an accurate shot traveling a shorter distance may still be much closer to the hole than an inaccurate shot traveling a much longer distance. Nevertheless, for the purpose of this discussion distance and accuracy will be treated as distinct.
Maximizing distance requires, among other things, efficient transfer of energy from the club head to the ball at impact. One factor affecting the energy transfer is the material used to make the club head. When making a wood club head from wood, designers select a hard wood, traditionally either persimmon or laminated maple, and more recently have provided metallic strike face inserts to increase energy transfer. Recent improved manufacturing techniques have allowed construction of hollow woods made entirely of metal, particularly of titanium and stainless steel, providing marked improvements over their wooden counterparts. Even though improved, hollow metal woods can experience a certain amount of uncontrolled deformation away from the strike face, especially in the larger oversize heads, which can contribute to degrading the club head/ball energy transfer.
Another factor affecting distance is the "loft" of the club, which determines the trajectory of the ball after impact. There are several factors that determine the "loft" or trajectory of a ball upon impact. The first is the loft angle. It is readily apparent that a larger loft angle will result in a higher trajectory. The location the club head's center of mass relative to that of the ball, measured vertically up from the sole plate also affects the trajectory. All else being equal, a club head with a lower center of mass will result in a higher trajectory. If the center of mass of the club head is above that of the ball, it will produce a much lower trajectory and the ball will carry much less distance. Another factor affecting trajectory is the dynamic loft which, among other things, is determined by shaft flexibility and location the club head's center of mass measured horizontally from the club face. The average player has difficulty obtaining the desired ball trajectory, and thus difficulty in achieving the desired distance, when using a driver or other wood club because these clubs have traditionally had a relatively small loft angle high and forward center of mass.
A factor affecting accuracy is the resistance of the club head to rotate about a vertical axis passing through the club head's center of mass, otherwise known as the moment of inertia. For example, the dynamic forces generated through the swing result in torque being applied to the shaft which can result in excessive opening of the club face. Also, if at impact the ball strikes on line with the center of mass there will be little or no twisting about this point. However, if as in many cases, the ball strikes off the center of mass towards the heel or toe of the club head, the club head will tend to rotate about the center of mass imparting side spin to the ball causing it to stray from its intended path. Light weight, high strength materials, such as titanium, have enabled club manufacturers to increase the size of the club head, thereby increasing the moment of inertia of the club head and to some extent addressing these difficulties. Oversized club heads have unquestionably done very well in the market place.
Different designs have been attempted to address various aspects of the difficulties described above. For example, U.S. Pat. No. 5,720,674 discloses a golf club head with a high density peripheral strip around the club head behind the strike face. It is asserted in the disclosure that the arrangement combines "the effect of stabilization during rotation and dynamic loft." In another design, disclosed in U.S. Pat. No. 5,785,605, an oversized metal wood head is disclosed in which recesses are positioned in the bottom wall in order to add "bottom wall strength and stiffness." Another club which is available on the market, the "Crane Magic Wand", attempts to address some of the previously discussed deficiencies by positioning a weight on the back of a relatively large club head.
In spite of the various attempts, the prior art has not achieved a head design which successfully combines the various aspects of club performance. There thus remains a need in the art for a hollow metal wood club with improved moment of inertia, energy transfer and dynamic loft achieved without otherwise significantly altering overall mass or excessively increasing the volume of the club head.